There is a trend in multi-carrier mobile communication consumer equipment towards the provision of multimode wireless services using various standards which are continuously being updated. As the demand for personalised applications suited to diverse needs continues to grow, there is an increasing need for multimode terminals which can provide seamless connectivity between different multi-carrier modes and which can be upgraded according to user needs.
One widely used mode of implementing multi-carrier communications is the use of Orthogonal Frequency Division Multiplexing (OFDM). OFDM is a spread spectrum modulation technique which distributes data over a large number of carriers which are spaced apart at precise frequencies. Because of the fact that OFDM subcarrier pulses are chosen to be rectangular, the task of pulse forming and modulation can be performed by a simple Inverse Discrete Fourier Transform (IDFT) which can be efficiently implemented using an Inverse Fast Fourier Transform (IFFT) block. In the wireless domain, OFOM is used in the newer forms of IEEE 802.11 wireless LAN (WLAN) designs and in the IEEE 802.16-2004 (WiMAX) specifications for metropolitan area networking. It has also recently been proposed as the basis for successors to 3G cellular communication systems. In the wired area, OFDM is referred to as discrete multi-tone (DMT) and is the basis for the ADSL standard.
Another multi-carrier communication mode which is being considered for future standards is the Digital Wavelet Multi-Carrier (DWMC) system. Although more costly to implement, DWMC does provide several advantages over OFDM, specifically in regard to Additive White Gaussian Noise channel performance, Raleigh fading channel performance and Signal to Noise Ratios (SNR). Pulse forming and modulation in DWMC systems is performed using the Inverse Wavelet Transform (IWT).
IWT and IFFT based systems each have their own advantages and disadvantages. IFFT systems are inexpensive and have grown into an industry standard, while IWT based systems show better performance in most situations. This has created a need for a multimode transceiver design which can be used for future Inverse Wavelet Transform (IWT) based systems as well as legacy systems based on the Inverse Fast Fourier Transform (IFFT). The industry has responded to this need by producing multimode transceiver terminals which can support both IFFT and IWT mode operation.
However, conventional multimode terminals employ fixed Application Specific Integrated Circuits (ASICs) for each mode. This implementation is not cost effective in that at least one dedicated ASIC needs to be designed for each of the IFFT and IWT modes. Also, the presence of multiple dedicated ASICs increases the size of the transceivers. Furthermore, due to design rigidity, ASICs based multimode transceivers cannot be upgraded or reconfigured.
Thus, because of the current progressive shift in certain areas of wireless services from IFFT based to IWT based systems and the bulkiness and high cost of current multimode systems, there is a clear need for a multi-mode transceiver design which uses shared resources to implement both IFFT and IWT based communication modes.